The literature is replete with attempts to reclaim gold from ores and coarse mixtures which contain this precious metal in varying amounts.
Various filter systems have been proposed but these have proven unsuccessful because the gold and the refuse have essentially identical particle sizes and the filter cannot selectively separate one particle from another. As a result, the filters soon become coated with a mixture of both gold and refuse and meaningful recovery is made impossible to achieve.
In U.S. Pat. No. 443,901 E. Craig describes an apparatus for separating gold and silver from ores by subjecting the mixture to a column of horizontally moving air so that the particles are blown into separate bins each according to its own weight and specific gravity.
Unfortunately, the Craig apparatus relates solely to the treatment of low-grade ores and it has no application to finely powdered mixtures. Moreover, Craig requires that air jets be directed upwardly through the ore so as to avoid the premature deposit of particles into the receiving bins.
The use of air jets may be necessary or desirable in separating large ore pieces but such means is counterproductive in separating finely divided particles from one another because the turbulence which they create makes it impossible for the particles to settle out in collectible quantities.
L. Soulages describes in U.S. Pat. No. 244,114 a system for separating heavy ore components from lighter ones by directing a draft of air across a flowing stream of ore. The heavier components fall into a first hopper and the lighter particles fall into succeeding hoppers.
This apparatus relies solely upon gravity separation and it is useful where large ore pieces are sought to be graded but it has no application in the case of finely divided particles.
In U.S. Pat. No. 366,923 E. Butler also directs air against a stream of ore but, again, no effluent is formed and there is no provision for separating and collecting gold particles from a mixture of finely divided components.
Accordingly, neither filter systems or the known gravity-type separators are capable of separating gold particles from mixtures in which the components are all present in a finely divided form.